ISC(2) added Third party management. Took a few minutes to find.
Looking at the ISC(2) Store and seeing the original six domains listed I will tell you that the CBK is probably more than enough to get you started if you read everything in the bibliography as well as the intro pages or text of the book.
The exam was very straight forward when you have at least 2 years of experience in healthcare. Suspect the Third Party Management section will be straight forward enough that you should easily find enough best practices to more than makeup for the lack of published information in the CBK.
I did this test right out of beta with nothing more than the downloadable syllabus from which to work and did just fine. Its a practitioner exam and nowhere near as difficult as the CISSP (still easy with experience).
My observation on publishing new CBK books tells me your in for a long wait. Probably another 9-12 months minimum if not longer. So I wouldn't hold up on taking the exam if you have the experience and read the existing CBK, you should be just fine.